Normal service was resumed at the Etihad as City moved to within a point of the top with Haaland taking his tally for the season to 22.
The Norwegian failed to score for the first time in 10 games at club level at Anfield last weekend, but quickly made amends by showing his immense pace and power to latch onto Ederson's long ball, round Robert Sanchez and barrel Adam Webster off the ball to tap into an empty net.
Haaland then smashed home his 17th Premier League goal of the campaign from the penalty spot.
Brighton are still to win under new boss Roberto De Zerbi but did push the champions back after the break when Leandro Trossard fired in at the near post.
But another piece of City brilliance, this time from Kevin De Bruyne, killed the game off as the Belgian curled in from outside the box.